Dental products and procedures

ABSTRACT

Polymeric shells which fit over one or more natural teeth to change the perceived color of the teeth, and optionally to provide orthodontic support. The shells can be prepared by thermoforming selected polymeric sheets which contain optical additives over a physical image of the teeth, or by depositing polymeric compositions containing optical additives over a physical image of the teeth, or by additive manufacturing based upon a digital image of the teeth. The optical additives cause the combination of the shell and the teeth to have a desired appearance. At least part of the shell preferably has transparency greater than 75%, particularly greater than 85%.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 15/849,678, filed Dec. 21, 2017, which is a continuation of U.S. application Ser. No. 14/381,202, filed Aug. 26, 2014 (now U.S. Pat. No. 9,918,813 issued Mar. 20, 2018), which is an application under the 35 USC 371 based on International Application No. PCT/US 2013/027950, which claims priority from U.S. Provisional Application No. 61/634,370, filed Feb. 27, 2012. This application claims priority from U.S. application Ser. No. 14/381,202, filed Aug. 26, 2014, International Application No. PCT/US 2013/027950, filed Aug. 26, 2014, and U.S. Provisional Application No. 61/634,370, filed Feb. 27, 2012. The entire disclosure of each of the afore-mentioned applications is incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The present disclosure relates to products and procedures for changing the appearance of teeth.

BACKGROUND

Many products and procedures have been used, or proposed for use, in order to change or modify teeth in the human mouth. In orthodontic procedures, the objective is to change the relative positions of two or more teeth. In some cosmetic procedures, the objective is to change the perceived color of teeth so that the teeth appear whiter.

One orthodontic procedure makes use of one or more rigid polymeric shells each of which fits over the teeth and, when in place, does not fit precisely to one or more of the teeth and, therefore, imparts a displacing force to the teeth and over the course of time changes the relative positions of two or more teeth. Reference may be made for example to U.S. Pat. No. 5,975,893 (Chishti) and U.S. Pat. No. 7,220,122 (Chishti), the entire disclosure of each of which is incorporated herein by reference. Many polymers, including some of those used in dental and orthodontic applications, have a slightly yellow color which is produced during manufacturing or processing such as extrusion, injection molding and/or thermoforming. Consequently, although the primary objective of the rigid polymeric shell is functional, it often contains a small quantity of additives to change the yellow color. This is referred to as “color compensation” or “color correction”.

Much effort and expense has been expended in order to whiten teeth. However, the known cosmetic procedures have substantial disadvantages. Many cosmetic procedures make use of bleaching agents which are applied directly to the teeth; bleaching agents can damage the natural tooth structure itself and/or can produce different cosmetic effects on the natural tooth structure and/or stains and/or fillings and/or crowns. Other cosmetic procedures make use of compositions which form a coating on top of the teeth; those compositions are difficult to apply uniformly and accurately, and degrade relatively rapidly and/or are difficult to remove. For information about known cosmetic procedures, reference may be made for example to U.S. Pat. Nos. 3,986,261, 4,032,627, 5,716,208, 6,343,933, 6,368,576, 6,503,485, 6,986,883 and 7,214,262, and US Patent Publications 2005/0175552 and 2007/0086960, the entire disclosure of each of those patents and patent publications is incorporated herein by reference for all purposes

SUMMARY

I have discovered, in accordance with the present invention, new products and procedures for changing the perceived color of teeth. In some embodiments of the invention, the products and procedures also change the relative positions of two or more teeth. Throughout this specification, the terms tooth and teeth includes natural teeth, including natural teeth which have been modified by fillings or by crowns, implanted teeth, artificial teeth that are part of a bridge or other fitting secured to one or more natural or implanted teeth, and artificial teeth that are part of a removable fitting.

In a first aspect, this invention provides a self-supporting shell which fits over one or more teeth and which is composed of a polymeric composition comprising a polymer and one or more optical additives which cause the combination of the shell and the teeth to have a desired appearance. The term “optical additive” is used herein to mean an additive which substantially changes the color or light transmission properties of the polymeric composition.

In a second aspect, this invention provides a method of providing a desired change in the appearance of teeth which comprises placing a self-supporting shell according to the first aspect of the invention over one or more teeth.

In a third aspect, this invention provides a method of making a self-supporting shell according to the first aspect of the invention, the method comprising forming a selected polymeric composition into a shape which will fit over the teeth over which the shell is to be placed, the selected polymeric composition preferably having been selected by assessing the color of the teeth over which the shell is to be fitted and, based on that assessment, selecting the polymeric composition from a range of polymeric compositions of different colors.

In a fourth aspect, this invention provides a method which comprises

-   -   (A) assessing the color of teeth over which a self-supporting         shell according to the first aspect of the invention is to be         placed,     -   (B) selecting from a range of compositions having different         colors, a composition which will provide a desired change in the         appearance of teeth when formed into a self-supporting shell         according to the first aspect of the invention, and     -   (C) forming the selected composition into a self-supporting         shell.

In a fifth aspect, this invention provides a method which comprises

-   -   (A) selecting, from a set of colored samples, a sample which         matches the color of teeth to be treated, and     -   (B) correlating the selected sample with a polymeric composition         which, when formed into a self-supporting shell and placed over         the teeth will give the teeth a desired appearance.

In a sixth aspect, this invention provides a sheet of a polymeric composition for use in the method of the third or fifth aspect of the invention, for example by thermoforming the sheet around a physical model of the teeth over which the shell is to be fitted.

In a seventh aspect, this invention provides a set of sheets of a polymeric composition, the sheets being (i) composed of different compositions containing different amounts of optical additives, and (ii) being such that they can be formed into a self-supporting shell according to the first aspect of the invention. There can be, for example, at least 2, at least 3, at least 4, preferably at least 5, e.g. 5-20 identical samples of each of the different sheets.

In an eighth aspect, this invention provides a novel polymeric composition for use in the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in the accompanying drawings. The FIGURE shows the color ranges which are often observed for discolored teeth (area A), normal teeth (area B) whitened teeth (area C), orthodontic appliances (area D), and a preferred color range for tooth shells of this invention (area E). In the FIGURE, on the horizontal axis, the negative values relate to green colors and the positive values relate to red colors, and on the vertical axis, the negative values relate to blue colors and the positive values relate to yellow colors.

DETAILED DESCRIPTION

In the Summary of the Invention above and in the Detailed Description of the Invention below, including the Examples and illustrations, reference is made to particular features of the invention. It is to be understood that the disclosure of the invention in this specification includes all possible combinations of such particular features. For example, where a particular feature is disclosed in the context of a particular aspect or a particular embodiment, that feature can also be used in combination with other particular aspects and embodiments, and in the invention generally, except where the context excludes that possibility. The invention disclosed herein include embodiments not specifically described herein and can for example make use of features which are not specifically described herein, but which provide functions which are the same, equivalent or similar to, features specifically disclosed herein.

The term “comprises” and grammatical equivalents thereof are used herein to mean that, in addition to the features specifically identified, other features are optionally present. For example, a composition or device “comprising” (or “which comprises”) components A, B and C can contain only components A, B and C, or can contain not only components A, B and C but also one or more other components. The terms “consisting essentially of” and grammatical equivalents thereof are used herein to mean that, in addition to the features specifically identified, other features may be present which do not materially alter the claimed invention. The term “at least” followed by a number is used herein to denote the start of a range beginning with that number (which may be a range having an upper limit or no upper limit, depending on the variable being defined). The term “at most” followed by a number is used herein to denote the end of a range ending with that number (which may be a range having 1 or 0 as its lower limit, or a range having no lower limit, depending upon the variable being defined). When a range is given as “(a first number) to (a second number)” or “(a first number)-(a second number)”, this means a range whose lower limit is the first number and whose upper limit is the second number. The terms “plural”, “multiple”, “plurality” and “multiplicity” are used herein to denote two or more than two features.

Where reference is made herein to “a” or “an” feature, this includes the possibility that there are two or more such features (except where the context excludes that possibility). Where reference is made herein to two or more features, this includes the possibility that the two or more features are replaced by a lesser number or greater number of features providing the same function, except where the context excludes that possibility. The numbers given herein should be construed with the latitude appropriate to their context and expression; for example, each number is subject to variation which depends on the accuracy with which it can be measured by methods conventionally used by those skilled in the art.

This specification incorporates by reference all documents referred to herein and all documents filed concurrently with this specification or filed previously in connection with this application, including but not limited to such documents which are open to public inspection with this specification.

Parts, percentages and ratios given in this specification are by weight unless otherwise noted.

Unless otherwise noted, the term color measurement is used herein to refer to measurements made using the LAB CIE color scale wherein L refers to total reflected light, A refers to the Red (+)-Green (−) color Axis and B refers the Yellow (+)-Blue (−) color axis measured using a D65 light source (daylight). However, color can also be measured using the CYMK scale which makes use of digital images. Other color measurement systems are known and any suitable method may be used in evaluating products of this invention.

The term pigment is used herein to denote a solid particulate coloring agent which can be mixed with a polymer.

The term dye is used herein to denote a coloring agent that is soluble or molecularly dispersed in a polymer.

The term fluorescent agent is used herein to denote a material that absorbs light in one region of the spectrum and emits light in the same or different region of the spectrum. The emission may be almost immediate or may be delayed.

The term light transmission is used herein to denote the amount of light passing through a sample. Unless otherwise stated, transmission refers to visible light as measured by a method similar to ASTM D1003-11 Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics. Light transmission may also be measured using a colorimeter and a white reference sample, in which case the measurement includes two passages of light through the sample.

The term incident light is used herein to denote light which shines onto an object and which may be reflected, scattered or least partially absorbed by the object.

The term reflected light is used herein to denote incident light which reflects off the surface of an object after impinging on the object.

The term scattered light is used herein to denote light which diverges from a straight path after it has impinged on an object.

The term light scattering particles is used herein to denote particles having a size from about 0.2 to about 20μ and which are transparent or substantially white. By white is meant that the particles do not absorb significant amounts of light in the range from about 400 nm to about 700 nm.

The term thermoplastic polymer is used herein to denote a polymer which is relatively hard at a lower temperature, which becomes relatively soft when subjected to heat and pressure, and again becomes relatively hard when cooled, provided that the heat and pressure do not chemically decompose the polymer.

The term thermosetting polymer is used herein to denote a polymeric composition which is a solid or viscous material at a relatively low temperature and which, when subjected to heat and/or suitable radiation, and/or when the material undergoes one or more chemical reactions, changes irreversibly into an infusible polymer network. The term thermoset polymer is used to denote a cured thermosetting polymer.

The Polymer in the Polymeric Composition.

The polymer in the polymeric composition in the self-supporting shell used in the present invention can be a homopolymer, or a random, block or a graft copolymer. The composition can contain a single polymer or a mixture of two or more polymers. Generally, the polymer is substantially transparent, so that the optical characteristics of the self-supporting shell are dominated by the optical additives which are mixed with the polymer, but the invention includes the possibility that the polymer is a semicrystalline polymer which scatters light.

The polymer can optionally have one or more of the following characteristics (i.e. a single one of the following characteristics or any possible combination of two or more of the following characteristics).

-   -   (1) The polymer comprises a thermoplastic polymer.     -   (2) The polymer comprises a thermoset polymer.     -   (3) The polymer is an elastomer, preferably an elastomer having         elongation to break greater than 200% and a 100% modulus of less         than 3000 PSI (value for D50 or less TPU)     -   (4) The polymer is a polyester, for example a polyethylene         terephthalate glycol polymer (PETG), e.g. one of the polyesters         sold by Eastman Chemical under the trade names Eastar and         Durastar, or one of the polyesters sold by DuPont under the         trade name Hytrel.     -   (5) The polymer is a polyurethane, for example a rigid         polyurethane such as that sold by Lubrizol Corporation under the         trade name Isoplast, or a thermoplastic polyurethane (TPU) such         as one of those sold by Lubrizol Corporation under the trade         name Pellethane, by Merquinsa under the trade name Pearlthane,         by BASF under the trade name Elastollan, and by Bayer under the         trade name Texin.     -   (6) The polymer is a polyolefin, including high-density         polyethylene, low density polyethylene, medium density         polyethylene, linear low density polyethylene; a copolymer of         ethylene and one or more comonomers, e.g. comonomers selected         from the group consisting of other α-olefins, vinyl acetate,         acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate         and butyl acrylate; polypropylene, e.g. clarified polypropylene;         a propylene copolymer, e.g. a clarified propylene copolymer;         polystyrene; a copolymer of styrene and one or more comonomers,         e.g. comonomers selected from the group consisting of acrylic         comonomers, acrylonitrile, acrylonitrile and butadiene,         including block copolymers of styrene with ethylene, ethylene         and propylene, isoprene and butadiene; polymers of cyclic         olefins; and polymethyl pentene.     -   (7) The polymer is an acrylic or methacrylic resin, including         polyacrylonitrile and copolymers of acrylonitrile.     -   (8) The polymer is an aliphatic or aromatic or mixed aliphatic         aromatic polyamide, a polycarbonate, a polyether, an ionomer         resin or a cellulose ester or ether.     -   (9) The polymer is a fluoropolymer, e.g. polyvinylidene         fluoride, fluorinated ethylene propylene, polyvinyl chloride, or         the product sold under the tradename Kynarflex.

The Additives in the Polymeric Compositions.

The polymeric composition can contain a single optical additive or a mixture of two or more optical additives. The polymeric composition can contain other additives which are not optical additives. The optical additives may be one or more optical additives selected from the group consisting of pigments, dyes, light scattering particles and fluorescent materials.

The optical additive can optionally have any one of the following characteristics, or any possible combination of one or more of the following characteristics.

-   (1) The optical additive, when dispersed in a sample of the     polymeric composition having a thickness of 0.76 mm, preferentially     absorbs light within the range from about 550 to about 700 nm, such     that, when measured against a reference white sample (e.g. a white     color tile) using conditions D65, the LAB color values for the     combination of the white color tile and the polymer sheet have an L     value of between about 18 and 95, an A value from about −2 to +2 and     a B value from about −1 to −10. -   (2) The optical additive comprises a pigment or dye having a color     which ranges from blue to violet, for example ultramarine blue,     ultramarine violet, manganese oxides, phthalocyanine, violet 92,     violet 11C, blue 385, blue 214, blue 30C591, blue 30C588, FDC blue     #1, blue 214. Other blue and violet pigments which can be used     include the following (which are listed by their CI name) PB 1, PB     1:2; PB 9, PB 15; PB 15:1, PB 15:2, PB 15:3, PB 15:4, PB 15:6, PB     15:34; PB 16, PB 17, PB 24, PB 25, PB 27, PB 28, PB 29, PB 30, PB     31, PB 34, PB 35; PB 36; PB 36:1, PB 60, PB 61, PB 61:1, PB 62, PB     63, PB 66, PB 68, PB 71, PB 72, PB 73, PB 74, PB 75, PB 76, PB 79,     PB 80, PB 81, PB 82, PB 84, PB 128, PV 1, PV 1:1,PV 1:2, PV 2, PV     2:2, PV 3, PV 3:1, PV 3:3 PV 5, PV 5:1, PV 7, PV 13, PV 14, PV 15,     PV 16, PV 18, PV 19, PV 23, PV 25, PV 27, PV 29, PV 31, PV 32, PV     36, PV 37, PV 39, PV 42, PV 44, PV 47, PV 48, PV 49, PV 50, PV55, PV     58, and PV 17. -   (3) The optical additive comprises a red pigment or die, for example     NR 1. NR 2, NR 3, NR 4, NR 6, NR 8, NR 9, NR 10, NR 11, NR 12, NR     16, NR 20, NR 22, NR 23, NR 24, NR 25, NR 26, NR 28, NR 31, PR 1, PR     2, PR 3, PR 4, PR 5, PR 6, PR 7, PR 8, PR 9, PR 12, ;PR 13, ;PR 14,     PR 15, PR 17, PR 19, PR 21, PR 22, PR 23, PR 31, PR 32, PR 38, PR     39, PR 47, PR 48, tPR 48:1, PR 48:2, PR 48:3, PR 48:4, PR 49, PR     49:1, PR 49:2, PR 52:1, PR 52:2, PR 53, PR 53:1, PR 57, PR 57:1, PR     57:2, PR 58:4, PR 60, PR 60:1, PR 61, PR 62, PR 63, PR 63:1, PR 69,     PR 81, PR 81:1, PR 81:2, PR 81:3, PR 81:4, PR 83, PR 83:1, PR 83:3,     PR 85, PR 88, PR 89, PR 90, PR 90:1, PR 101, PR 101:1, PR 102, PR     103, PR 104, PR 105, PR 106, PR 107, PR 108, PR 108:1, PR 109, PR     112, PR 113, PR 113:1, PR 114, PR 119, PR 120, PR 121, PR 122, PR     123, PR 139, PR 144, PR 146, PR 147, PR 148, PR 149, PR 150, PR 160,     PR166, PR 168, PR 169, PR 170, PR 170:1, PR 171, PR 172, PR 173, PR     174, PR 175, PR 176, PR 177, PR 178, PR 179, PR 180, PR 181, PR 183,     PR 184, PR 185, PR 187, PR 188, PR 190, PR 192, PR 193, PR 194, PR     200, PR 202, PR 204, PR 206, PR 207, PR 208, PR 209, PR 210, PR 211,     PR 212, PR 213, PR214, PR 216, PR 221, PR 223, PR 224, PR 226, PR     230, PR 231, PR 232, PR 233, PR 235, PR 236, PR 238, PR 239, PR 242,     PR 243, PR 245, PR 251, PR 252, PR 253, PR 254, PR 255, tPR 256, PR     257, PR 258, PR 259, PR 260, PR 262, PR 264, PR 265, PR 266, PR 268,     PR 269, PR 270, PR 271, PR 272, PR 273, PR 274, PR 275, PR 276, PR     279, PR 282, PR 286, PR 287, PR 288, and PR 571. -   (3) The optical additive comprises light scattering (reflecting)     particles, preferably light scattering particles which, when a     sample of the polymeric composition having a thickness of 0.76 mm is     exposed to natural light, from about 5% to about 50%, preferably 5     to 25%, of the incident light is reflected. Suitable light     scattering particles include titanium dioxide, barium sulfate,     calcium carbonate, boron nitride, silica, mica, and spherical glass     particles. The presence of such an additive in the shell tends to     mask the natural color of the teeth (which usually has a yellowish     and/whole yellowish red tint) because a portion of the incident     light is reflected before it is absorbed by the teeth. If the amount     of reflected incident light is less than about 5%, the improvement     is slight, whereas if the amount of reflected incident light is     greater than about 50%, the perception of the underlying tooth     structure may be reduced to a level such that the teeth are not     perceived as natural.

Light scattering occurs when there is a difference between the refractive index of the particles and the polymer in which they are dispersed. The greater the difference in refractive index, the greater the degree of scattering. If the particles are transparent to the incident light in the wavelengths of interest, then essentially all of the light will be reflected or will pass through. If the particles absorb light in one or more ranges of wavelength, then the polymeric composition will be perceived as having a color which contains a reduced amount of those wavelengths. If the proportion of light reflecting particles is high and substantially all the incident light is scattered, the composition will appear white. At lower levels, the composition may appear translucent and light going through it will be “diffuse”. For use in this application it is generally desired that any light scattering particles added do not absorb light, so they do not contribute to off color or increase of the gray value of the teeth. In some cases it is desirable to utilize particles that are sufficient to cause light scattering, while maintaining a high degree of total light transmission.

It has been found that appropriate use of light-scattering particles can not only result in teeth which look whiter, but can also mask areas of teeth having different colors, for example stained regions or darker areas near the base of the teeth, resulting in a more uniform and cosmetically desirable appearance.

-   (4) The optical additive comprises a fluorescent material which     absorbs ultraviolet light having a wavelength of less than about 400     nm and which emits light in the range from about 400 to about 600     nm. These fluorescent materials are also referred to as brightening     agents. Optionally the fluorescent material can also absorb light     having a wavelength in the range from about 550 to about 700 nm.     Dyes and/or pigments cause selective absorption of light such that     the reflected light is more equally balanced across the visible     spectrum (more equal amounts of each primary color); as a result,     the presence of dyes and/or pigments in the shell make the perceived     tooth color closer to white, but also reduces the total amount of     light reflected, so that the teeth do not appear as bright.     Fluorescent materials, by absorbing light outside the visible     spectrum and emitting light in the purple-blue-green region of the     visible spectrum, can make the teeth appear both whiter and     brighter. Many fluorescent materials are known and have a wide range     of chemical structures. They include for example triazine-stilbenes,     coumarins, imidazolines, diazoles, triazoles, benzooxazolines and     biphenyl-stilbenes. Specific optical brighteners include the     materials designated by the CAS number 7128-64-5, 1533-45-5,     2397-00-4, 5089-22-5, 40470-68-6, 13001-38-2, 13001-39-3,     58449-88-0, 13001-40-6, 16470-24-9, 2226-96-2, 4193-55-9, 27344-41-8     and 16090-02-1.

Polymeric Compositions.

The polymeric composition in the self-supporting shells used in the present invention comprises a polymer, for example a polymer as disclosed above, and an optical additive, for example an additive as disclosed above. In some cases, it is preferable that the composition, when in the form of a uniform sheet having a thickness of 0.5 mm, has a total transmission of greater than about 80% and a diffuse transmission greater than about 50%, when measured by ASTM D 1003.

For the best results, which in most cases means teeth which are natural looking and as white as is desired by the individual whose teeth are being treated, the selection of the optical additives will be made in conjunction with inspection of the teeth onto which the shell it is to be placed. It is not at present practical to formulate a special composition for each individual. But it is practical to formulate a relatively limited number of “standard” compositions from which those skilled in the art, having regard to their own knowledge and the disclosure in this specification, will be able to select a composition which is likely to give excellent results.

Those skilled in dentistry are familiar with the ways in which the color of teeth can be assessed, and the selection of a material for a filling or a crown to match the natural color of teeth. Common tooth colors are often designated by a combination of a letter (usually A-D) and a number (usually 1-4), with A, B, C and D designating different hues (A red yellow, B yellow, C gray, and D red yellow gray), and 1-4 designating the color intensity. The designations M1, M2 and M3 are typically used to denote highly bleached teeth. Alternatively, the color of teeth can be measured by a colorimeter. Having determined the color of the teeth to be covered by the self-supporting shell, one skilled in the art will select a shell material which, when converted into a shell and placed over the teeth, will result in covered teeth which are perceived to have the desired color (which will normally be substantially whiter than the natural color of teeth), and which will preferably completely or partially disguise any staining of the teeth. For example, if a tooth having (on the VITA scale) a B 4 color is covered with a shell having (on the LAB scale) A and B values of 2.5 and −5, the tooth will appear from about 1 to about 4 shades lighter. It should be noted that the color of the shell material will not be the perceived color of the covered teeth, since the perceived color will depend on both the underlying natural color of the tooth, the color of the shell material and the type of incident illumination. Preferably the color of the natural teeth is at least one shade lighter is according to the VITA scale than the color of the same teeth without the shell.

Preparation of the Polymeric Compositions and of Polymeric Sheets Comprising Those Compositions.

The polymeric compositions used in this invention, and polymeric sheets comprising those compositions, can be prepared by conventional methods which are well-known to those skilled in the art of polymer technology.

Polymeric Sheets for Conversion into Self-Supporting Polymeric Shells

It will often be convenient for the self-supporting polymeric shells to be produced by shaping a polymeric sheet of a desired composition. The polymeric sheet can optionally have any one of the following characteristics, or any possible combination of one or more of the following characteristics.

-   1. It is a flat sheet having a uniform thickness of 0.10-2 mm,     preferably 0.15-1.5 mm. -   2. It is a flat sheet whose outer periphery is circular, oval or     rectangular (including square), for example with an area of 10-100     in.² -   3. It is a flat sheet having dimensions such that it will completely     cover a model of the teeth in the upper jaw or the lower jaw of an     adult, or of a child, for example a flat sheet which is a circular     disk, a flat sheet which is part (for example half) of a circular     disk. -   4. The polymeric composition is the same throughout the sheet. -   5. The polymeric composition varies from top to bottom of the sheet.     For example, the concentration of the additive (or one or more of     the additives) is different at different levels going through the     thickness of the sheet, including the possibility that there is no     additive (or none of one or more of the additives) at one or more     levels. -   6. The sheet is a laminate having two or more layers of different     polymeric compositions, for example (1) a laminate which contains an     optical brightener in a layer which, when the sheet is formed into a     self-supporting shell, is not part of the exterior surface of the     shell, for example in a layer which is the central layer of a three     layer laminate, or (2) a laminate which comprises (i) a first layer     which, when the sheet is formed into a self-supporting shell, is in     contact with the teeth, and which contains a first concentration of     an optical additive, and (ii) a second layer which, when the sheet     is formed into a self-supporting shell, is exposed, and which is     free from the optical additive or which contains a second     concentration of the optical additive, the second concentration     being substantially less than the first concentration, for example     not more than 0.2 times the first concentration. The polymers in the     different layers are generally the same but can be different. -   7. The sheet has a variable thickness such that when the sheet is     thermoformed over a model of the teeth, each part of the     thermoformed sheet has a thickness of at least 0.1 mm, at least 0.15     mm, at least 0.2 mm or at least 0.3 mm, and a thickness of at most     1.5 mm, preferably at most 1 mm., preferably a thickness in the     range of 0.2 to 1.0 mm. -   8. The sheet has a color within the area E as shown in the FIGURE. -   9. The sheet contains substantially no fluorescent agent and has     values of L, A and B on the LAB scale when the sheet is measured on     a white color tile, as shown in the following table.

L A B Preferred 75 to 99 −3 to 6 −10 to −1  More preferred 80 to 99 −2 to 5 −7 to −1 Particularly preferred 85 to 99 −1 to 5  −5 to −1.5 Since the value of L is the total light (L being 100), the added coloring agents will always reduce L to less than 100 if the sheet contains no fluorescent agent. In some embodiments, the sheet has a value of L greater than about 85, a value of A greater than about −0.5 and less than about 6.0, and a value of B from about −1.0 to −15.0.

-   10. The sheet contains a fluorescent agent and optionally other     optical agents, and has values of L, A and B on the LAB scale when     the sheet is measured on a white color tile, using a light source     that includes light with a frequency of about 300 to about 400 nm     (UV) and is filtered to D65, as shown in the following table.

L A B Preferred 75 to 110 −3 to 6 −10 to −1  More preferred 80 to 110 −2 to 5 −7 to −1 Particularly preferred 85 to 110 −1 to 4  −5 to −1.5 In some embodiments, L is greater than about 85, A is −1.0 to 6.0, and B is −1.0 to −10.0, preferably −1.0 to −5.0.

-   11. The sheet has a transparency of greater than 75%, preferably     greater than 85%. -   12. The sheet is in the form of a roll, 5-6 inches (127-152 mm)     wide, and 50-100 feet (15-30 m) long -   13. A plurality of sheets, e.g. 20, 50, 100 or 500 sheets, are     packaged together. -   14. The sheet has a moisture content of less than 1%, preferably     less than 0.5%. -   15. The sheet is prepared by a process which comprises drying under     control conditions which prevent discoloration of the sheet.

The Self-Supporting Polymeric Shells

The self-supporting shells can be prepared in any appropriate way. In one embodiment, the shell is prepared by shaping a sheet comprising the polymeric composition, for example by thermoforming the sheet over a model of the teeth to which the shell is to be fitted.

The First and Second Aspects

The self-supporting shell must fit closely to at least a major part of the front of the teeth over which it is placed, and preferably fits closely to a substantially the entire surface of the teeth over which it is placed. Generally, the shell will be one which can be removed by the wearer simply by pulling the shell off the teeth (which may be desirable for example when eating or for conventional tooth cleaning). However, the invention includes the possibility that the shell is secured to the teeth in some more permanent fashion.

The shell optionally has one of the following characteristics, or any possible combination of one or more of the following characteristics.

-   (1) The average thickness of the shell is at least 0.1 mm,     preferably at least 0.15 mm, and at most 1.5 mm. When the only     purpose of the shell is to change the appearance of the teeth, the     average thickness is preferably at most 0.5 mm or at most 0.4 mm.     When the shell is also used as part of an orthodontic procedure, for     example a retainer or other dental appliance, the average thickness     of the shell is greater, for example at least 0.5 mm or at least 0.6     mm. -   (2) When the shell is prepared by thermoforming a polymeric sheet of     uniform thickness, the thickness of the shell will vary from place     to place, depending upon the amount of deformation of the sheet     during the thermoforming process. When the only purpose of the     thermoformed shell is to change the appearance of the teeth, it     generally has a thickness which is at least 0.06 mm, at least 0.08     mm, at least 0.1 mm or, at least 0.2 mm, at least 0.3 mm, at least     0.4 mm at least 0.5 mm, at least 0.6 mm, or at least 0.7 mm, and a     thickness of at most 1.0 mm or most 0.8 mm. When the thermoformed     shell is also used as part of an orthodontic procedure, it generally     has a thickness which is at least 0.5 mm, at least 0.6 mm, and the     0.7 mm, at least 0.8 mm, at least 0.9 mm, at least 1.0 mm, at least     1.1 mm, at least 1.2 mm, at least 1.3 mm, or at least 1.4 mm, and a     thickness of at most 1.5 mm. When the only purpose of the shell is     to change the appearance of the teeth, it preferably has a thickness     in the range of 0.2 to 0.06 mm, particularly in the range of 0.3 to     0.5 mm. When the thermoformed shell is also used as part of an     orthodontic procedure, it preferably has a thickness of the range of     0.3 to 1.0 mm, particularly in the range of 0.5 to 0.8 mm.

The shell can be prepared by thermoforming a polymeric sheet which is not of uniform thickness, for example a polymeric sheet which has a greater thickness in the areas which will be deformed by the thermoforming.

When the only purpose of the shell is to change the appearance of the teeth, the polymeric composition can have a flexural modulus of less than 1000 MPa or less than 800 MPa. When the shell is also used as part of an orthodontic procedure, the polymeric composition preferably has a flexural modulus of more than 1000 MPa, preferably more than 1500 MPa, e.g. 1000-3000 MPa.

-   (2) The polymeric shell comprises one or more optical additives. The     concentration of the additives which modify the optical properties     of the shell can be greater near the surface of the tooth than it is     further from the surface of the tooth. For example, the polymer at     the surface of the shell remote from the surface of the tooth can be     substantially free of the optical additives. When the optical     additive is uniformly dispersed in the shell, there is often a     “fattening” effect which tends to make the teeth appear to extend to     the outer surface of the shell. In an extreme case, where the outer     surface of the shell is white and opaque, only the relatively flat     outer surface of the shell is perceived, and the surface of the     actual teeth is not perceived. In a preferred embodiment, the     colored part of the shell (or she) would be no more than about 0.5     mm thick, preferably no more than about 0.25 mm thick, and in some     cases less than 0.1 mm. -   (3) At least a portion of the shell has a total visible light     transmission greater than about 75% and a LAB transmission value,     when measured on a white tile, of L greater than or equal to 85, A     from about −1.0 to about 6, preferably about −1 to about 3, and B     from about −1.0 to about −15, preferably about −1.0 to −5.0. -   (4) At least a portion of the thermoformed shell extends over the     gum line (beyond the upper or lower edge of the teeth). When the     portion of the thermoformed shell which extends over the gum line     has a total visible light transmission greater than about 75%, the     portion of the shell that extends over the gum line is essentially     not visible.

The Third Aspect

The third aspect of the invention preferably makes use of a polymeric composition which is selected by assessing the color of teeth over which the shell is to be fitted, the selection being made from a range of polymeric compositions of different colors. However, the invention includes the possibility that the composition is one of a number of “standard” colors. The assessment of the color of the teeth can be carried out by a dentist and the selection of the appropriate polymeric composition can be carried out by the dentist or by another party at a different location.

Any method can be used to make the selected polymeric composition into a shape which will fit over the teeth whose appearance is to be changed. Since the compositions cannot be shaped over the teeth themselves, the first step is to make a digital or physical image which corresponds to the teeth. A physical image can be made by forming an impression of the teeth, for example using an alginate composition, and then forming the physical image in the mold provided by the impression. A physical image can also be made from a digital image.

One method of making the self-supporting shell is to thermoform a sheet of the polymeric composition over a physical image of the teeth. Another method of making the self-supporting shell is to form the polymeric composition on the physical image of the teeth, for example by spraying, painting or deposition. The polymer can be a thermoplastic polymer or a thermosetting polymer which is cured, for example with ultraviolet light, after it has been formed into the desired shape.

Another method of making the self-supporting shell is to create it by a stereolithographic process (three dimensional printing) based upon a digital image of the teeth.

The Fourth Aspect

The fourth aspect of the invention includes the steps of (A) assessing the color of teeth over which the shell is to be placed, and (B) based on the assessment in step (A), selecting a composition from a range of compositions having different colors. The method can also include, as a preferred step, (C) forming the selected composition into a self-supporting shell. These steps can be carried out by the same person (usually a dentist); or each of the steps can be carried out by a different person; or steps A and B can be carried out by the same person (usually a dentist) and step C carried out by a different person; or step A can be carried out by one person (usually a dentist) and steps B and C carried out by a different person.

The Fifth Aspect

The fifth aspect of the invention is a method which comprises

-   -   (A) selecting, from a set of colored samples, a sample which         matches the color of teeth to be treated, and     -   (B) correlating the selected sample with a polymeric composition         which, when formed into a self-supporting shell and placed over         the teeth will give the teeth a desired appearance.

In a first embodiment of the fifth aspect of the invention, the samples are (i) sized so that they can be placed against teeth within a human being's mouth, (ii) have a range of colors which correspond to the natural colors of teeth, and (iii) are correlated with different compositions containing different amounts of optical additives such that polymeric compositions correlated with the samples, when formed into self-supporting shells according to the first aspect of the invention, will give the teeth a desired appearance. The set of samples can be a known set of samples except that the samples are correlated with different compositions which when formed into a self-supporting shells, will give teeth a desired appearance. The set of samples can for example contain at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, or at least 10, for example at least 20, e.g. 20-50 different samples. The set of samples can be supplemented by photographs or digital images which will show how the teeth will appear after they have been fitted with a shell made of the correlated polymeric composition.

In a second embodiment of the fifth aspect of the invention, the samples are thin colored polymeric strips which have a similar thickness to a self-supporting shell and a range of colors which are the same as the available colors for the self-supporting shells. These strips will show the human being a good simulation of the tooth color that will be obtained when a self-supporting shell made of the selected colored strip is placed over the teeth.

The Sixth Aspect

The sixth aspect of the invention provides a sheet of a polymeric composition for use in the method of the third or fifth aspect of the invention, for example by thermoforming the sheet around a physical model of the teeth over which the shell is to be fitted.

The Seventh Aspect

The seventh aspect of the invention provides a set of sheets of a polymeric composition, the sheets (i) being composed of different compositions containing different amounts of optical additives, usually compositions which are identical except for the content of the optical additives, and (ii) being such that they can be formed into a self-supporting shell according to the first aspect of the invention. There can be, for example, at least 2, at least 3, at least 4, preferably at least 5, e.g. 5-20 identical samples of each of the different sheets.

The Eighth Aspect

The eighth aspect of the invention provides novel polymeric compositions for use in the invention. The compositions can have some or all of the characteristics set out above.

Use of the Invention When a Tooth is Missing.

When a tooth is missing, the absence of the tooth is conventionally disguised by making a bridge which contains an artificial tooth (a so-called “pontic”). This invention provides an alternative way of compensating for the absence of a tooth. The shell can be formed with a section corresponding to the missing tooth, and the interior of that section of the shell can be partially or completely coated and/or filled with a filling material having substantially the same color as the natural teeth. It has been found that it is significantly easier to match the color of the filling material to the natural teeth when using a shell of this invention than it is to match the color of a pontic to the color of the natural teeth.

Use of the Invention to Provide Orthodontic as well as Cosmetic Improvements.

If desired, one or more parts of the self-supporting shell can be offset from the natural position of one or more teeth, so that when the shell is in place, it exerts a force on one or more teeth which moves the teeth in a desired direction, for orthodontic purposes. In this use, the shell needs to be more rigid than is necessary, or even desirable, for a shell which has only a cosmetic purpose. For example, for orthodontic appliance, it is desirable to use a polymeric sheet which, before being thermoformed, is 0.5 to 0.8 mm thick and for the polymeric composition to have a flexural modulus between 1000 and 3000 MPa.

EXAMPLES Example 1

The compositions A-F of Table 1 were prepared from tinted and non-tinted rigid polyurethane. CPU 664 and Zendura A are tinted. Isoplast 2530 is not tinted.

Thickness Composition (millimeters) L color A color B color A- CPU 664 0.82 74.85 9.92 −20.7 B- CPU 664 0.28 88.4 4.46 −9.01 C- CPU 664 0.16 92.39 2.72 −5.15 D- Zendura A 0.77 95.9 0.45 −0.18 E- Isoplast 2530 0.81 97.47 −0.07 1.44 F - Isoplast 2530 0.8 94.5 −0.24 6.22 Normal Tooth Range 68 0.5 15 Reference tooth colors for “normal range teeth” are taken from the literature

An impression was made of an individual's upper teeth using alginate and converted into a positive model using dental plaster. A sheet of polyurethane (composition C) having a thickness of 0.16 mm was thermoformed over the positive plaster model, trimmed and cleaned. A second shell was prepared using a longer heating cycle resulting in a slightly thinner shell. These shells are designated UB-1 and UB-2 respectfully.

The natural teeth of individual A were examined in sunlight and were found to have the same color. The shell UB-1 was then applied only to the upper teeth, and the upper and lower teeth photographed in sunlight. When the upper shell of Example 1 was placed on the upper teeth, it was observed that the upper teeth were significantly whiter than the lower teeth.

The shell UB-2 was applied only to the upper teeth of individual A, and the upper and lower teeth photographed in sunlight.

Color analysis of the right incisor in the upper teeth of the shell UB-2 and the natural color of the right incisor was conducted using a computer drawing program and is reported in Table 2.

TABLE 2 Color of Right Incisor with and Without Shell Color of Right Incisor Cyan Magenta Yellow Black No shell 0 11 24 8 Shell 0 14 16 16 It can be noted that the yellow value was reduced from 24 to 16. In this example the UB-1 shell slightly over-corrected the original tooth color. It is estimated that a preferable initial value for the tinted plastics sheet would have a LAB color value of approximately; L=97, A=1.0, B=−2.0

Example 2

Samples A-G as shown in Table 3 below were prepared by mixing Styrene co-polymer K Resin BK10 (Chevron Phillips, LLC) with the ingredients and amounts thereof shown in Table 3. The ingredient OB-1 in Table 3 is the optical brightener 2,2-(1,2-ethenediyldi-4, 1-phenylene) bisbenzoxazole (Keystone Aniline Corporation). The ingredients were mixed in an internal mixer and pressed into sheets approximately 0.65 mm thick. The sheets were subsequently formed into shells as in Example 1 and applied to the upper teeth of Individual A.

TABLE 3 Composition of K-Resin Formulations. Ultra- Ultra- marine marine OB-1 Blue Violet Barium Titanium Sample Designation (%) (%) (%) Sulfate Dioxide A BM79-38-A 0.01% B BM79-38-B 0.01% 0.01% 0.05% C BM79-38-C 0.02% D BM79-39-A 0.015% 1% E BM79-39-B 0.015% 1% 0.2% F BM79-39-C .005% 0.03% G BM79-39-D .006% 0.05% The color values of Individual A's right incisor when covered with Shells A, B and C, UB-1 and UB-2 and two controls (two separate measures of the color value of the Individual A's right incisor with no cover over it) were measured, and the results are shown in Table 4 below.

TABLE 4 Measured Color Values Con- Con- Con- Shell Shell Shell Shell Shell trol-1 trol 2 trol Av UB-1 UB-2 A B C Cyan 0 0 0 0 0 0 0 0 Magenta 12 11 11.5 14 8 11 10 12 Yellow 28 25 26.5 16 12 19 15 17 Gray 11 15 13 16 7 12 12 12 Total 51 51 51 46 27 42 37 41 CYMK The shell prepared from composition E was opaque (<50% light transmission) and judged to be less desirable as a tooth whitening shell as the opacity of the shell masks the spaces between the teeth such that individual teeth are not as apparent as desired. However, the shell of composition E has value when it is desired to mask the absence of a tooth, such as when a pontic is used.

The shell prepared from composition G (BM 79-39-D) was evaluated in bright daylight and in diffuse light, and the results are shown in Table 5. As would be expected, the specific colors values vary with type and amount of light. Table 5 shows the color values of Individual A's right incisor when covered with shell prepared from composition G, and the control (the color value of the Individual A's right incisor with no cover over it).

TABLE 5 Evaluation of Shell From Composition BM79-39-D Control- Bm79-39-D Control BM79-39-D Sun Sun Shade Shade Cyan 0 0 0 0 Magenta 15 7 24 18 Yellow 23 14 49 28 Gray 19 12 28 34 The color data in both types of lighting show a dramatic reduction in yellowing and improvement in tooth color.

Example 3

PETG resin (Eastar 6763) is combined with ultramarine blue and ultramarine violet pigment master batch and extruded into a sheet of thickness 0.07 mm the amount of the pigment being such that the sheet has LAB color values measured on a white color tile of L=94, A=1.3, B=−2.5. A dental impression is made from an individual's upper and lower teeth using a plastic dental tray and alginate resin. Dental stone is prepared by mixing 100 grams of plaster with 24 grams of water and poured into the alginate mold and allowed to set. The plaster model is removed and cleaned. Disks are prepared from the extruded sheet by die cutting samples 125 mm in diameter and dried at 80 C for 2 hours. The dried discs are pressure-formed over the plaster models using a Biostar thermoformer manufactured by distributed by Great Lakes Dental. The thermoformed parts are removed from the plaster models, trimmed to the gum line and cleaned. Color measurements are made on the individual's teeth before and after the shells are placed over the teeth.

The following statements define particular aspects of the invention.

-   Statement 1. A shell which is composed of a polymeric composition     containing an optical additive and which contains cavities shaped to     cover a plurality of teeth, the shell having an average thickness of     from 0. 1 mm to 1.5 mm, preferably 0.2 to 1.5 mm, and a transparency     of greater than 75%, preferably greater than 85%, the observed color     of the teeth when they are covered by the shell (i) being     substantially less yellow than the color of the teeth without the     shell, and/or (ii) the observed color of teeth when they are covered     by the shell being at least one shade lighter, according to a tooth     color classification system, than the color of the same teeth     without the shell, and/or (iii) the observed color of the teeth when     they are covered by the shell being brighter than the color of the     same teeth without the shell. -   Statement 2. A shell according to Statement 1 wherein the polymeric     composition is based on a polymer selected from the group consisting     of polyolefins, e.g. polyethylene, polyesters, including for example     copolymers such as polyethylene terephthalate glycol resins (PETG),     polyurethanes including rigid polyurethanes, thermoplastic     polyurethanes (TPU), polypropylene and propylene copolymers, acrylic     and methacrylic resins and co-polymers, polystyrene and co-polymers     including random and block co-polymer and elastomers and     fluoropolymers. -   Statement 3. A shell according to Statement 1 or Statement 2 wherein     the optical additive comprises one or more of a pigment, a dye,     light scattering particles and a fluorescent material with optical     properties. -   Statement 4. A shell according to Statement 1 or Statement 2 wherein     the optical additive is selected from the group consisting of     ultramarine pigments, ultramarine blue, ultramarine violet,     cobalt-based pigments and resin soluble dyes. -   Statement 5. A shell according to Statement 1 or Statement 2 wherein     the optical additive comprises a material selected from the group     consisting of titanium dioxide, barium sulfate, calcium carbonate,     silica, mica and zinc oxide. -   Statement 6. A shell according to Statement 1 or Statement 2 wherein     the optical additive comprises a fluorescent material which absorbs     light with a wavelength of less than 390 nm and emits light with a     wavelength of from 400 nm to 600 nm. -   Statement 7. A shell according to Statement 1 or Statement 2 wherein     the optical additive comprises a fluorescent material and a pigment     or dye that absorbs light in the range of from about 550 nm to about     700 nm. -   Statement 8. A shell according to any one of Statements 1 to 5 which     does not contain a fluorescent agent and which, when not fitted over     teeth, and measured on the LAB scale on a white color tile, has an L     value from 50 to 99, preferably 75 to 99, more preferably 80 to 99,     particularly preferably 85 to 99, an A value of −1 to 10, preferably     −3 to 6, more preferably −2 to 5, particularly preferably −1 to 5     e.g. 0.5 to 5, and a B value of −1 to −14, preferably −10 to −1,     e.g. −10 to −2, more preferably −7 to −1, particularly preferably −5     to −1.5. -   Statement 9. A shell according to any one of Statements 1-7 wherein     the optical additive comprises a fluorescent agent and which, when     not fitted over the teeth, and measured on the LAB scale on a white     color tile and using a light source that includes light with a     frequency of about 300-400 nm filtered to D65 has an L value from 75     to 110, preferably 80 to 110, more preferably 85 to 110,     particularly preferably 85 to 99, an A value of −3 to 6, more     preferably −2 to 5, particularly preferably −1 to 4, and a B value     of −10 to −1, more preferably −7 to −1, particularly preferably −5     to −1.5. -   Statement 10. A shell according to any one of Statements 1-9 wherein     from about 10% to about 50% of the incident light is reflected from     the shell rather than the underlying tooth. -   Statement 11. A shell according to any one of Statements 1-10     wherein the shell provides orthodontic treatment to the teeth. -   Statement 12. A shell according to any one of Statements 1-11     wherein the shell comprises two or more layers, and the outermost     layer contains a lower concentration of optically active materials     than another layer. -   Statement 13. A shell according to Statement 12 wherein the     outermost layer is 0.2 to 0.7 mm thick. -   Statement 14. A sheet of a polymeric composition which can be     thermoformed into a shell according to any one of Statements 1-13. 

1. A self-supporting shell which (a) can be fitted over one or more teeth to change the perceived color of the one or more teeth, and (b) comprises two or more levels, at least one of the levels being a first level comprising a polymeric composition comprising a polymer and a first concentration of one or more optical additives, and at least one other second level comprising a polymeric composition comprising a polymer, the second layer (i) comprising one or more optical additives in a second concentration which is different from the first concentration or (ii) being free from optical additives.
 2. A self-supporting shell according to claim 1 which comprises two or more layers, at least one of the layers being a first layer comprising a polymeric composition comprising a polymer and a first concentration of one or more optical additives, and at least one other second layer comprising a polymeric composition comprising a polymer, the second layer (i) comprising one or more optical additives in a second concentration which is different from the first concentration or (ii) being free from optical additives.
 3. A self-supporting shell according to claim 2 which comprises (1) a first layer which is not on the outside of the shell when the shell is fitted over the one or more teeth and which contains a first concentration of the one or more optically active additives, and (2) a second layer which (i) is on the outside of the shell when the shell is fitted over the one or more teeth and (ii) contains a second concentration of the one or more optically active additives, the second concentration being less than the first concentration.
 4. A self-supporting shell according to claim 1 wherein the shell comprises a laminate comprising a layer which (i) contains an optical brightener and (ii) is not part of the exterior surface of the shell.
 5. A self-supporting shell according to claim 1 which is for use in an orthodontic procedure and which has a flexural modulus of more than 1500 MPa.
 6. A self-supporting shell according to claim 5 which has a thickness of 0.5 to 0.8 mm.
 7. A self-supporting shell according to claim 1 which is for use in changing the appearance of the tooth or teeth and which has a flexural modulus of less than 800 MPa.
 8. A self-supporting shell according to claim 7 which has a thickness of 0.2 to 0.6 mm.
 9. A self-supporting shell according to claim 1 which has an innermost level having a total visible light transmission greater than about 75%.
 10. A self-supporting shell according to claim 9 which has been applied over the tooth or teeth, and the innermost level of the shell extends over a gum line beyond the upper edge of the teeth and/or the lower edge of the teeth.
 11. A method of making a self-supporting shell according to claim 1 which comprises depositing a succession of polymeric compositions onto a physical image of the tooth or teeth.
 12. A method of making a self-supporting shell according to claim 1 by three-dimensional printing based on a digital image of the teeth.
 13. A sheet which can be thermoformed over a model of one or more teeth to provide a self-supporting shell which can be fitted over one or more teeth to change the perceived color of the one or more teeth, the sheet comprising two or more levels, at least one of the levels being a first level comprising a polymeric composition comprising a polymer and a first concentration of one or more optical additives and at least one second level comprising a polymeric composition which (a) has a second concentration of one or more optical additives, the second concentration being different from the first concentration, or (b) is free from optical additives.
 14. A sheet according to claim 13, wherein there is no additive at one or more levels in the sheet.
 15. A sheet according to claim 13 wherein the polymeric composition is based on a polymer selected from the group consisting of elastomers, polyesters, polyurethanes, polyolefins, acrylic resins, methacrylic resins, polyamides, polycarbonates, polyethers, ionomer resins, cellulose esters, cellulose ethers and fluoropolymers.
 16. A sheet according to claim 13 wherein the one or more optical additives comprises light-scattering particles selected from the group consisting of one or more of titanium dioxide, barium sulfate, calcium carbonate, boron nitride, silica, mica and zinc oxide, and the concentration of at least one of the optical additives is different at different levels going through the thickness of the sheet.
 17. A sheet according to claim 13 wherein the sheet is a laminate having two or more layers of different polymeric compositions, and the laminate contains an optical brightener in a layer which, when the sheet is thermoformed, is not an exterior surface of the shell.
 18. A sheet according to claim 13 wherein the sheet is a laminate having two or more layers of different polymeric compositions and the laminate comprises (i) a first layer which has a first concentration of an optical additive, and (ii) a second layer which provides an exterior surface of the laminate and is free from the optical additive or which contains a second concentration of the optical additive, the second concentration being substantially less than the first concentration.
 19. A polymeric sheet according to claim 13 which has a uniform thickness of 0.10-2 mm and which comprises a polymer and one or more optical additives, wherein the concentration of the one or more optical additives is different at different levels going through the thickness of the sheet, and the one or more optical additives comprise one or more light-scattering particles selected from the group consisting of titanium dioxide, barium sulfate, calcium carbonate, boron nitride, silica, mica and zinc oxide.
 20. A polymeric sheet according to claim 13 which has a uniform thickness of 0.10-2 mm and which has an exterior level having a transparency of greater than 85%. 